media: doc: media/v4l-drivers: Add Qualcomm Camera Subsystem driver document
Add a document to describe Qualcomm Camera Subsystem driver. Signed-off-by: Todor Tomov <todor.tomov@linaro.org> Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
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Todor Tomov
Mauro Carvalho Chehab
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.. include:: <isonum.txt>
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Qualcomm Camera Subsystem driver
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================================
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Introduction
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------------
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This file documents the Qualcomm Camera Subsystem driver located under
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drivers/media/platform/qcom/camss-8x16.
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The current version of the driver supports the Camera Subsystem found on
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Qualcomm MSM8916 and APQ8016 processors.
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The driver implements V4L2, Media controller and V4L2 subdev interfaces.
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Camera sensor using V4L2 subdev interface in the kernel is supported.
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The driver is implemented using as a reference the Qualcomm Camera Subsystem
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driver for Android as found in Code Aurora [#f1]_.
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Qualcomm Camera Subsystem hardware
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----------------------------------
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The Camera Subsystem hardware found on 8x16 processors and supported by the
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driver consists of:
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- 2 CSIPHY modules. They handle the Physical layer of the CSI2 receivers.
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A separate camera sensor can be connected to each of the CSIPHY module;
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- 2 CSID (CSI Decoder) modules. They handle the Protocol and Application layer
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of the CSI2 receivers. A CSID can decode data stream from any of the CSIPHY.
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Each CSID also contains a TG (Test Generator) block which can generate
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artificial input data for test purposes;
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- ISPIF (ISP Interface) module. Handles the routing of the data streams from
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the CSIDs to the inputs of the VFE;
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- VFE (Video Front End) module. Contains a pipeline of image processing hardware
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blocks. The VFE has different input interfaces. The PIX input interface feeds
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the input data to the image processing pipeline. Three RDI input interfaces
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bypass the image processing pipeline. The VFE also contains the AXI bus
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interface which writes the output data to memory.
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Supported functionality
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-----------------------
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The current version of the driver supports:
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- input from camera sensor via CSIPHY;
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- generation of test input data by the TG in CSID;
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- raw dump of the input data to memory. RDI interface of VFE is supported.
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PIX interface (ISP processing, statistics engines, resize/crop, format
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conversion) is not supported in the current version;
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- concurrent and independent usage of two data inputs - could be camera sensors
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and/or TG.
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Driver Architecture and Design
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------------------------------
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The driver implements the V4L2 subdev interface. With the goal to model the
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hardware links between the modules and to expose a clean, logical and usable
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interface, the driver is split into V4L2 sub-devices as follows:
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- 2 CSIPHY sub-devices - each CSIPHY is represented by a single sub-device;
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- 2 CSID sub-devices - each CSID is represented by a single sub-device;
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- 2 ISPIF sub-devices - ISPIF is represented by a number of sub-devices equal
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to the number of CSID sub-devices;
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- 3 VFE sub-devices - VFE is represented by a number of sub-devices equal to
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the number of RDI input interfaces.
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The considerations to split the driver in this particular way are as follows:
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- representing CSIPHY and CSID modules by a separate sub-device for each module
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allows to model the hardware links between these modules;
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- representing VFE by a separate sub-devices for each RDI input interface allows
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to use the three RDI interfaces concurently and independently as this is
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supported by the hardware;
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- representing ISPIF by a number of sub-devices equal to the number of CSID
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sub-devices allows to create linear media controller pipelines when using two
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cameras simultaneously. This avoids branches in the pipelines which otherwise
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will require a) userspace and b) media framework (e.g. power on/off
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operations) to make assumptions about the data flow from a sink pad to a
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source pad on a single media entity.
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Each VFE sub-device is linked to a separate video device node.
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The complete list of the media entities (V4L2 sub-devices and video device
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nodes) is as follows:
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- msm_csiphy0
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- msm_csiphy1
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- msm_csid0
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- msm_csid1
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- msm_ispif0
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- msm_ispif1
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- msm_vfe0_rdi0
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- msm_vfe0_video0
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- msm_vfe0_rdi1
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- msm_vfe0_video1
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- msm_vfe0_rdi2
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- msm_vfe0_video2
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Implementation
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--------------
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Runtime configuration of the hardware (updating settings while streaming) is
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not required to implement the currently supported functionality. The complete
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configuration on each hardware module is applied on STREAMON ioctl based on
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the current active media links, formats and controls set.
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Documentation
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-------------
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APQ8016 Specification:
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https://developer.qualcomm.com/download/sd410/snapdragon-410-processor-device-specification.pdf
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Referenced 2016-11-24.
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References
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----------
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.. [#f1] https://source.codeaurora.org/quic/la/kernel/msm-3.10/
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